Showing papers on "Epichloë published in 2010"

Defensive mutualism between plants and endophytic fungi

Abstract: Endophyte-grass symbiosis is generally considered to be a classic example of microbe-plant symbiosis in which the fitness of the microbial symbiont and its host plant is closely linked, and thus, presumed to align the interests of partners toward mutually beneficial cooperation. Accumulating evidence seems to suggest that defensive mutualism provides the best framework for understanding plant-endophyte interactions in general. We conducted a meta-analysis of 99 published studies on 36 plant (inc. both grass and tree species), 62 herbivore and 17 predator or parasitoid taxons to test the importance of defensive mutualism in multitrophic interactions. In general, statistical perusal revealed that we still know little about these seemingly well-studied biological interactions. The conceptual framework for endophyte-grass interactions has largely been based on endophyte-plant-herbivore studies of two, economically important, artificially selected and introduced agricultural grass species, tall fescue and perennial ryegrass, and two generalist invertebrate pests. Only 10 original publications provided data of higher trophic levels. Consistent with the defensive mutualism hypothesis, the meta-analysis indicates that endophytes slightly increase grass resistance to herbivores, and the defensive mutualism appears to be most commonly detected in systemic and vertically transmitted grass endophytes compared to horizontally transmitted tree endophytes. However, variation appears to increase when higher trophic levels are considered. In addition to taxonomical bias, the literature is strongly biased toward short-term laboratory and greenhouse experiments rather than field conditions. Thus, current literature is insufficient to capture the breadth of variability inherent in the wild grass-endophyte populations and communities, and the general importance of defensive mutualism remains to be solved in future studies.

The Epichloae, Symbionts of the Grass Subfamily Poöideae1

Abstract: Symbioses of grasses (Poaceae) with fungi of family Clavicipitaceae vary widely in relative benefits and detriments to the plant, and include mutualisms characterized by vertical transmission and protective effects of the fungus and its metabolites against vertebrate and invertebrate herbivores. This review focuses on the epichloae, a group of fungi within the Clavicipitaceae that are symbiotic with members of the grass subfamily Pooideae and comprise sexual fungi of genus Epichloe (Fr.) Tul. & C. Tul. and their asexual derivatives (form genus Neotyphodium A. E. Glenn, C. W. Bacon & R. T. Hanlin). Most epichloid fungi are vertically transmissible, and many produce antiherbivore alkaloids belonging to any of four distinct chemical classes: lolines, peramine, ergot alkaloids, and indole-diterpenes. Like many plant-associated Clavicipitaceae, fruiting of Epichloe species chokes host inflorescences, preventing seed production on the affected tillers. However, most Epichloe-infected grasses also produ...

Managing plant symbiosis: fungal endophyte genotype alters plant community composition

Abstract: Summary 1. Understanding the extent to which plant genotype influences community composition has important conservation and management value. Here, we add a new layer to current research by testing whether genotypes of plant symbionts influence plant community composition. 2. Tall fescue grass Lolium arundinaceum is planted worldwide for forage, turf, and soil stabilization, has invaded native communities, and commonly hosts the foliar endophytic fungus, Neotyphodium coenophialum. We quantified vegetation development over a 6-year period in replicated field plots of the two most commonly introduced genotypes of the endophyte (KY-31, AR-542) in two tall fescue cultivars (Georgia-5, Jesup). The KY-31 endophyte produces ergot alkaloids toxic to mammalian herbivores, while AR-542 lacks ergots. We expected that the KY-31 endophyte would promote tall fescue dominance by altering mammalian herbivory, that endophyte-free plots would support the highest plant diversity, and that AR-542 endophyte would show intermediate effects. 3. Plots with the KY-31 endophyte supported 10% fewer plant species than endophyte-free or AR-542 plots. KY-31 also reduced graminoids and forbs more strongly than AR-542, with the greatest response in Georgia-5. Endophyte genotype did not significantly alter the prevalence of tall fescue; however, absence of the endophyte reduced the biomass of Georgia-5. 4. Both plant and endophyte genetic identity influenced the persistence of endophyte symbiosis. In Georgia-5, the frequency of AR-542 declined more through time than did KY-31; these effects were reversed in Jesup. 5. Endophyte presence reduced herbivory by mammals (voles), but endophyte genotype had no effect, suggesting that voles were not driving endophyte genotype-mediated changes in plant composition, and that other compounds besides ergot alkaloids influenced vole feeding. 6. Synthesis and applications. When endophyte-symbiotic plants are desired, the AR-542 endophyte in the Georgia-5 background would achieve higher native plant diversity and reduce tall fescue invasion of nearby areas. Conversely, Jesup is recommended for increased tall fescue persistence, as both biomass and reproduction exceeded Georgia-5. In summary, our results demonstrate that, like plant genotype, symbiont genotype can also alter vegetation dynamics and plant composition and should be considered when managing for conservation, restoration, forage, turf, re-vegetation or soil stabilization.

The interplay between the effectiveness of the grass-endophyte mutualism and the genetic variability of the host plant.

Abstract: Neotyphodium endophytic fungi, the asexual state of Epichloe species, protect cool-season grasses against stresses. The outcomes of Neotyphodium-grass symbioses are agronomically relevant as they may affect the productivity of pastures. It has been suggested that the mutualism is characteristic of agronomic grasses and that differential rates of gene flow between both partners’ populations are expected to disrupt the specificity of the association and, thus, the mutualism in wild grasses. We propose that compatibility is necessary but not sufficient to explain the outcomes of Neotyphodium-grass symbiosis, and advance a model that links genetic compatibility, mutualism effectiveness, and endophyte transmission efficiency. For endophytes that reproduce clonally and depend on allogamous hosts for reproduction and dissemination, we propose that this symbiosis works as an integrated entity where gene flow promotes its fitness and evolution. Compatibility between the host plant and the fungal endophyte would be high in genetically close parents; however, mutualism effectiveness and transmission efficiency would be low in fitness depressed host plants. Increasing the genetic distance of mating parents would increase mutualism effectiveness and transmission efficiency. This tendency would be broken when the genetic distance between parents is high (out-breeding depression). Our model allows for testable hypotheses that would contribute to understand the coevolutionary origin and future of the endophyte-grass mutualism.

Do the costs and benefits of fungal endophyte symbiosis vary with light availability

Abstract: • Here, we examined whether fungal endophytes modulated host plant responses to light availability. First, we conducted a literature review to evaluate whether natural frequencies of endophyte symbiosis in grasses from shaded habitats were higher than frequencies in grasses occupying more diverse light environments. Then, in a glasshouse experiment, we assessed how four levels of light and the presence of endophyte symbioses affected the growth of six grass species. • In our literature survey, endophytes were more commonly present in grasses restricted to shaded habitats than in grasses from diverse light environments. • In the glasshouse, endophyte symbioses did not mediate plant growth in response to light availability. However, in the host grass, Agrostis perennans, symbiotic plants produced 53% more inflorescences than nonsymbiotic plants at the highest level of shade. In addition, under high shade, symbiotic Poa autumnalis invested more in specific leaf area than symbiont-free plants. Finally, shade increased the density of the endophyte in leaf tissues across all six grass species. • Our results highlight the potential for symbiosis to alter the plasticity of host physiological traits, demonstrate a novel benefit of endophyte symbiosis under shade stress for one host species, and show a positive association between shade-restricted grass species and fungal endophytes.

Gene expression profiling of the endophytic fungus Neotyphodium lolii in association with its host plant perennial ryegrass

Abstract: Endophytes of the Neotyphodium/Epichloe complex are filamentous fungi that typically form mutualistic associations with temperate grasses. The endophytes systemically colonise the intercellular spaces of their grass hosts and confer several biotic and abiotic attributes, but can also cause mammalian toxicoses. These symbioses are therefore of significant agricultural importance, and furthermore, the symbioses represent models to understand how such symbioses are established and maintained. To gain a greater understanding of the Neotyphodium lolii-perennial ryegrass (Lolium perenne) symbiosis, we have generated, sequenced and analysed four in planta expressed sequence tag libraries, enriched for genes differentially expressed during symbiosis via suppression subtractive hybridisation. Subtracted libraries were largely comprised of perennial ryegrass sequences, and comparative functional profiling of endophyte-infected ryegrass libraries with endophyte-free ryegrass libraries revealed downregulation of carbohydrate metabolism and photosynthesis during symbiosis, the latter confirming observations made in previous studies. Functional categories up regulated in the plant host in association with endophyte infection included cellular protein transport and protein synthesis and turn over.We also identified 24 N. lolii transcripts expressed during symbiosis, some of which were homologous to demonstrated pathogenicity/virulence genes, and others with proven roles in endophyte secondary metabolism. This study offers insights into biological processes underlying the N. lolii-perennial ryegrass symbiosis, and provides a list of novel candidate genes from both symbionts, which will form the basis for future investigations.

Genetic Diversity and Structure of Neotyphodium Species and Their Host Achnatherum sibiricum in a Natural Grass–Endophyte System

Abstract: Achnatherum sibiricum (Poaceae) is a perennial bunchgrass native to the Inner Mongolia Steppe of China. This grass is commonly infected by epichloe endophytes with high-infection frequencies. Previously, we identified two predominant Neotyphodium spp., N. sibiricum and N. gansuense. In the present study, genetic diversity and structure were analyzed for the two predominant Neotyphodium spp. as well as the host grass. We obtained 103 fungal isolates from five populations; 33 were identified as N. sibiricum and 61 as N. gansuense. All populations hosted both endophytic species, but genetic variation was much higher for N. gansuense than for N. sibiricum. The majority of fungal isolates were haploid, and 13% of them were heterozygous at one SSR locus, suggesting hybrid origins of those isolates. Significant linkage disequilibrium of fungal SSR loci suggested that both fungal species primarily propagate by clonal growth through plant seeds, whereas variation in genetic diversity and the presence of hybrids in both endophytic species revealed that although clonal propagation was prevalent, occasional recombination might also occur. By comparing genetic differentiation among populations, we found around 4–7-fold greater differentiation of endophyte populations than host populations, implying more restricted gene flow of endophytes than hosts. We proposed that endophyte infection of A. sibiricum might confer the host some selective advantages under certain conditions, which could help to maintain high-endophyte-infection frequencies in host populations, even when their gene flows do not match each other. Furthermore, we suggested that the same genotype of endophyte as well as host should be confirmed if the objective of the study is to know the influence of endophyte or host genotype on their symbiotic relationship, instead of just considering whether the plant is infected by an endophyte or not, since endophytes from the same host species could exhibit high levels of genetic diversity, which is likely to influence the outcome of their symbiotic relationship.

Grass Endophyte-Mediated Plant Stress Tolerance: Alkaloids and Their Functions

Abstract: The Family Clavicipitaceae (Hypocreales, Ascomycota) includes saprotrophic and symbiotic species associated with insects and fungi (Cordyceps spp.) or grasses, rushes and sedges (Balansia spp., Epichloe spp., Claviceps spp.) (Bacon and White, 2000). Symbiotic interactions are a notable feature of the Clavicipitaceae and they range in a continuum from antagonism to mutualism (Schardl et al., 2004). The plant biotrophic forms within this family can be characterized based on the nature of the association with hosts, being epibiotic during part or the entire life cycle or strictly endophytic with hyphae growing intercellular in the aboveground plant parts such as leaves, stems, and culms of the host.

Epichloë Endophytes: Models of an Ecological Strategy

Abstract: This chapter considers our current understanding of the epichloae, for which the recently sequenced Epichloe festucae is considered a model. The epichloae are in the family Clavicipitaceae within the order Hypocreales. While it was not the first recognition of an epichloe endophyte, the discovery of an introduced tall fescue population by University of Kentucky agronomists in the early 1930s led to the development of the (in)famously popular cultivar Kentucky-31. A flourish of studies comparing endophyte-infected (E+) and endophyte-free (E-) conspecific grasses in the 1980s and 1990s established a list of host fitness enhancements attributable to the endophyte: herbivore resistance, disease resistance, competitive ability, drought tolerance, heat tolerance, and tolerance to nutrient deficits. Researchers conducted a study to determine and compare the impacts of E+ and E- tall fescue on a natural grass community. The implications of this study reveal the concern that when introduced symbiota with pronounced fitness enhancements become established in nature, they run the risk of dominating communities and driving out some native plant species. While much of the understanding of ergot alkaloid biosynthesis has come from the characterization of the genes in the Claviceps spp., disruption and characterization of key pathway genes such as dmaW, lpsA, and lpsB have also been performed for epichloe endophytes. Most of the Epichloe and Neotyphodium endophytes screened to date are able to synthesize the alkaloid peramine.